Thanks to the constant progress in various technological fields, electronic elements in different electronic devices all have largely increased power and upgraded performance now. However, these electronic elements also produce a large amount of heat when they operate. The produced heat must be timely removed lest it should become accumulated in the electronic elements to result in raised temperature and adversely affected performance of the electronic elements. In some worse conditions, the accumulated heat would even cause failure or burnout of the electronic elements. To effectively solve the problem in connection with the heat dissipation of electronic elements, structures having better heat transfer efficiency, such as vapor chamber and thin heat pipe, have been successively introduced into market for use with heat sinks in an attempt to overcome at least the currently encountered heat dissipation-related problems.
The currently available thin heat pipe is formed by filling and sintering metal powder in a hollow space of a round pipe to form a wick structure on the round inner surface of the pipe, evacuating the pipe and then filling a working fluid in the pipe, and finally sealing and flattening the pipe to complete a thin heat pipe. It is noted, in the above-described thin heat pipe, the wick structure is distributed on the whole inner surface of a chamber formed in the thin heat pipe. When the working fluid is vaporized in the vaporizing section of the heat pipe, the vapor-phase working fluid diffuses to the condensing section at the other end of the heat pipe and is gradually cooled to finally become condensed into liquid-phase working fluid. With the help of the wick structure, the liquid-phase working fluid flows back to the vaporizing section again. However, since the chamber in the thin flat heat pipe is very narrow, the vapor-phase working fluid is hindered by the liquid-phase working fluid from smoothly and quickly flowing to the condensing section for cooling and dissipating heat.
Further, the wick structure in the condensing section forms a pressure resistance therein to adversely reduce the vapor-liquid circulation efficiency in the heat pipe, and part of the liquid-phase working fluid will become stagnated in the condensing section without flowing back to the vaporizing section to thereby largely reduce the heat transfer efficiency of the heat pipe.
Moreover, all the conventional thin heat pipes are manufactured to respectively have fixed cross sectional dimensions along their length and could not be configured according to actual needs to have different shapes and sizes at different positions, such as have one end with larger size and another end with smaller size, or have two equally sized ends but a gradually expanded or reduced middle portion. Besides, the wick structure, i.e. the sintered-powder structure, is always distributed on the whole inner surface of the conventional thin heat pipe. When the thin heat pipe is curved or bent to change its shape, the wick structure tends to be compressed or squeezed or even to separate from the inner surface of the thin heat pipe at the curved or bent position, which would no doubt largely reduce the heat transfer performance of the thin heat pipe. Since the wick structure is formed on the whole inner surface of the original round pipe without other changeful designs, when the round pipe is flattened to produce the thin heat pipe, the portions of the wick structure located at upper and lower parts of the inner surface of the thin heat pipe tend to become superposed and have increased thickness, which prevents the round heat pipe from being flattened by a largest possible extent and the flattening effect is limited.
The currently available vapor chamber includes a substantially rectangular case internally defining a chamber. A wick structure is formed on inner wall surfaces of the chamber and a working fluid is filled in the chamber. One side of the case is defined as a vaporizing area for attaching to a heat-producing element, such as a central processing unit (CPU), a south bridge chip or a north bridge chip, for absorbing the heat produced by the heat-producing element. The working fluid in a liquid phase located on the vaporizing area is heated and finally vaporized to become a vapor-phase working fluid, which moves and carries heat toward an opposite side of the case serving as a condensing area, at where the working fluid is cooled and converted into the liquid-phase working fluid again. The liquid-phase working fluid moves back to the vaporizing area under the effect of gravity or with the help of the wick structure to complete one cycle of vapor-liquid circulation in the vapor chamber and start another cycle. The vapor-liquid circulation in the vapor chamber continues to effectively achieve the purpose of lowering temperature and dissipating heat.
While the conventional vapor chamber can achieve the purpose of lowering temperature, it has another problem. That is, according to the working principle of the vapor chamber, the vaporizing area at one side of the case absorbs heat, which is transferred to the condensing area at the other side of the case by the working fluid in the chamber via change between vapor phase and liquid phase. More specifically, unlike the heat pipe that transfers heat to a distant position away from the heat source for dissipating, the vapor chamber achieves the heat dissipation effect simply by transferring heat from one side to the other side of the case instead of transferring the heat to a distant position, and is more suitable for uniform heat dissipation via a large surface area.